A 3D Refractive-Index Tomography (RIT), as a kind of optical technology which is proposed by E. Wolf and practiced by A. F. Fercher et al., may be employed in measuring optical characteristics and specimen (sample) patterns through measurement of 3D refractive-index distribution for semiconductor fabrication products or microscopic specimens (samples) such as cells [Non-patent documents 1 to 3]. The RIT may implement X-ray Computer Tomography (CT) by optics, by which a multiplicity of sheets of 2D holographic images (including optical absorption images and optical phase retardation images) is taken by changing general incident angles of plane waves on a sample and a 3D scattering potential is calculated from the multiplicity of 2D holographic images.
Conventionally, changing angles of plane waves is carried out by a galvanometer mirror [Non-patent document 2], or by a Liquid Crystal-based Spatial Light Modulator (LC-SLM).
However, those ways have some problems with speed and accuracy in measurement. For example, in a mode of directly rotating a sample, it has been difficult to fix a pivot of the sample and could be affected from vibration. Furthermore, if biological samples such as cells are directly rotating, there would be deformation of the samples.
In the case of employing a galvanometer mirror, it has been difficult to stably control incident angles due to microscopic vibrations and has not been allowable to complete exact optical alignment because of disagreement between a reflective surface and a pivot of the galvanometer mirror. Moreover, a LC-SLM is basically incapable of performing high-speed tomography due to a limit to response speed of liquid crystals, and very expensive to cause an increase of a unit product cost.